The present invention generally relates to apparatus and methods for disengaging generators and other rotating machines from an accessory such as a gearbox and, more particularly, to apparatus and methods of disengaging the rotating machine by using the existing permanent magnet rotor and permanent magnet stator of the rotating machine.
In the aerospace industry, aircraft receive electric power from generators. A permanent magnet exciter/generator (PME/G) is an essential part of the modern brushless aircraft generator. The PME/G is used to produce power for generator control units (GCU) once the generator is rotated with the prime mover. The generators also have main rotors, main stators, exciter rotors and exciter stators.
FIG. 1 show the basic operation of a prior art generator. In this prior art generator a permanent magnet rotor 61 rotates inside the electromagnet stator 62 windings to produce AC power sent from the stator 62 to the Generator Control Unit (GCU) 64 which senses output voltage and controls exciter stator current to keep output voltage constant. DC current is sent via wires 65 to the exciter stator 66 creating a static magnetic field cut by rotating exciter rotor windings 67. Rotating diodes 68 rectify the AC exciter rotor output. DC current in the main rotor windings 69 create a rotating magnetic field producing power in the main stator conductors 69a which transmit AC power from the main stator. FIG. 2 shows an exploded view of the prior art generator, from which one can appreciate that there are three sets of rotor and stator all on a single generator drive shaft 200: the exciter rotor 67 with the exciter stator 66, the main rotor 69 with the main stator 69aa and the permanent magnet rotor 61 with its electromagnet stator 62.
The generators are coupled to the main engine or to auxiliary power units through the gear box. Known designs of generators have a generator drive shaft that includes some kind of shear section that is based on safe operational capability of the gearbox. In the event that the generator malfunctions, this shear section operates and protects the gear box from continuing to rotate under an unacceptable load from a malfunctioning generator that may have stopped rotating. For constant speed generators, the design of the shear section is not difficult—it is easy to design a shear section to meet one speed. However, with the evolution of variable frequency generators (VFG), where failure can occur over a range of speeds, it is rather difficult to design a shear section that can protect the gear box regardless of the multiple possible speeds of the generator.
It is therefore useful that some other means should be incorporated into the design of the generator that would help protect the gear box. If, for example, there is a minor fault with the generator and it is not producing any power but rather is rotating like a load on the gear box, it is desirable that the generator be de-coupled from the gear box.
As can be seen, there is a need to de-couple the generator from the gear box as needed when the generator malfunctions. Furthermore, there is a need to have such a de-coupling mechanism that is re-settable by the operator or maintenance personnel of the aircraft when the problem with the generator is fixed or addressed. It is also required that the disconnect mechanism not disengage unnecessarily and not inadvertently engage when disconnected